1. Field of the invention.
The field of the invention relates to machinery for manufacturing pocketed coil springs as used in bedding and furniture.
2. Brief description of the prior art.
Assemblies of pocketed coil springs have been manufactured for a number of years. When employed as innerspring assemblies for mattresses and the like, they provide a comfortable sleeping or sitting surface. An example of such an innerspring construction is disclosed in U.S. Pat. No. 4,234,984. The patented construction includes a plurality of rows of pocketed coil springs connected to each other. The present invention is directed to an apparatus which manufactures such rows.
Prior to the introduction of ultrasonic bonding, a row of pocketed coil springs was manufactured by inserting compressed coil springs between opposed plies of a folded fabric strip and thereafter securing the plies transversely and longitudinally to form closed pockets. U.S. Pat. Nos. 1,733,660 and 1,813,993 disclose machines for forming pockets in this manner.
A relatively recent development has been the use of ultrasonically bondable pocketing material and equipment for thermally welding this material instead of sewing. Commonly assigned U.S. Pat. No. 4,439,977 is directed to an apparatus for thermally bonding plies of fabric together to form coil spring pockets. Means for compressing the springs and inserting them between the plies are also disclosed.